One of the most vexing problems that surgeons face when using surgical bone saws is the tendency of the saw to "kick" i.e., become caught upon the bone being cut by the point of the saw tooth. Another form of kicking occurs where the kerf has the same contour as the blade which is due to the fact that the cutting surface (i.e., teeth) lies on the same radius as the radius of tool rotation. In this scenario, all teeth grab nearly at the same time. This causes the saw apparatus to rotate about that point, transmitting a rotational force back through the saw and to the surgeon. This kicking or grabbing that occurs causes a loss of accuracy in the cut from the sudden, unpredictable movements of the saw and induces increased fatigue of the surgeon because of the greater tension that the surgeon must maintain in his hands and arms in anticipation of receiving this kicking or grabbing motion.
Another problem noted in existing blades involves the tendency of the saw to initially wander rather than to form a kerf. One reason for this involves the nature of oscillatory cutter blades. The handle portion of the saw remains stable because it is in the surgeon's control and remote from the cutting. However a blade (having a proximal end mounted into the oscillatory power tool) moves at a distal end that scribes an arc of a circle. Most surgical cutting saw blades have teeth on the distal extremity which are also oriented in an arc of constant radius. Especially when that arc has a geometrical center which coincides with the center of oscillatory motion, the bone to be penetrated is normally initially addressed by only one active cutting tooth in the series of teeth that resides on the arc, and as the blade completes its outward motion many teeth come into contact simultaneously. With several teeth contacting the bone, there is a greater tendency of the saw blade to kick and wander. The effect is even more pronounced when the blade teeth's center of arc is between the oscillatory center of the power tool and the blade's distal end.
Another problem involves the non-aggressive nature of prior art blades. Even when more than one tooth contacts the bone, it is primarily due to the manipulation of the blade by the surgeon. The effect is that adjacent teeth do not effect progressive cutting and therefore make binding and kick back more likely.
Moreover, once the kerf has formed, several other problems attend the cutting process. For one thing, substantially all the saw's teeth traverse along the entire extent, of the kerf. This decreases the aggressiveness of the cutting action as the cutting action is an abrading one rather than chipping. The teeth reside within the kerf for a longer period of time and tend to naturally generate more heat than had they been allowed outside the kerf. In addition, not having the teeth exit the working surface periodically tends to leave the chips of bone that have been abraded by the teeth to remain between the teeth. Lack of efficient chip removal is recognized as one cause of excessive heat generation. In surgical situations, such unwanted heat generation is undesirable because of thermal necrosis which damages bone structure adjacent to the cut.
The following documents reflect the state of the art of which applicants are aware and are tendered herewith to discharge the applicants' acknowledged duty to disclose relevant prior art of which they are aware. However, it is respectfully stipulated that none of these prior art teachings anticipate when considered singly or render obvious when considered in any conceivable combination the nexus of the instant invention as particularly detailed hereinafter.
______________________________________ INVENTOR PATENT NO. ISSUE DATE ______________________________________ Carroll 1948 Tuke 197505,105 Winter 1975,374 Bent 197643,934 Mongeon 1983609 Arnegger 198542 Arnegger 198699 ______________________________________ CATALOG TITLE ______________________________________ Micro-Aire .TM. Catalog "Accessories - Orthopedic Power Instrument System" Stryker .RTM. Surgical Catalog "Cutting Accessories Guide" Hall Surgical Catalog "Hall Quality Saw Blades for Stryker and 3M" ______________________________________
None of the prior art explicitly recognizes the value in having the teeth on an oscillatory cutter placed substantially on a tangent which is perpendicular to a radial line extending from the center of the power tools cutting axis that bisects the arc of travel within which the blade travels.